JP5515372B2 - Solid-state image sensor - Google Patents

Description

  The present invention relates to a solid-state imaging device.

  2. Description of the Related Art Conventionally, CMOS solid-state image sensors are known as solid-state image sensors applied to digital still cameras, video cameras, and the like. A pixel of a CMOS type solid-state imaging device has a photodiode, a floating diffusion region, an amplification transistor, and the like. The charge generated in the photodiode according to the amount of incident light is transferred to the floating diffusion region. The charge transferred from the photodiode is stored in the capacitance of the floating diffusion region, and a voltage corresponding to the charge is applied to the gate of the amplification transistor. A pixel signal corresponding to the amount of incident light is output from each pixel.

  Patent Document 1 discloses a configuration example of a CMOS solid-state imaging device in which a plurality of transistors having a common source and drain are formed by arranging gates on one active region, and the layout of transistors in each pixel is made efficient. Has been.

  Further, in the solid-state imaging device, when incident light penetrates from a semiconductor surface to a deep position and performs photoelectric conversion, the drift distance of electrons becomes long, so the probability that electrons reach a desired pixel is low. The above electrons can be absorbed even in a diffusion region (such as a floating diffusion region) having a higher potential, but crosstalk occurs when the electrons reach an adjacent pixel.

JP 2005-142503 A

  By the way, when the capacity of the floating diffusion region is small, a large voltage change can be obtained even with a small charge amount change. Therefore, if the capacity of the floating diffusion region is reduced in order to increase the gain of the pixel signal, the width of the gap that can be formed on the side of the floating diffusion region is widened. Since the charges generated in the vicinity of the gap are not absorbed in the floating diffusion region and easily reach adjacent pixels, there is a concern that crosstalk is likely to occur.

  Therefore, an object of the present invention is to provide means that can further suppress the occurrence of crosstalk in a solid-state imaging device.

The solid-state imaging device according to one aspect includes a first pixel and a second pixel that are arranged adjacent to each other in the first direction . The first pixel and the second pixel include a photoelectric conversion unit that generates a signal charge according to the amount of incident light, a floating diffusion unit that accumulates the signal charge generated by the photoelectric conversion unit, and a floating diffusion unit from the photoelectric conversion unit. And a transfer transistor for transferring the signal charge to each . Further, the transfer transistor of the first pixel and the floating diffusion portion of the first pixel are arranged between the photoelectric conversion unit of the first pixel and the photoelectric conversion unit of the second pixel. The transfer transistor of the first pixel is formed along one side extending in the second direction orthogonal to the first direction among the respective sides of the photoelectric conversion unit. The floating diffusion portion of the first pixel has a shape having a plurality of contact portions in contact with the transfer transistor of the first pixel at intervals in the second direction .

In the one aspect described above, the contact portions of the floating diffusion portion may be arranged so as to be symmetric with respect to the center of the side extending in the second direction of the photoelectric conversion portion.

  In the one aspect described above, the floating diffusion portion may be formed of a plurality of semiconductor regions each having a contact portion. And the capacity | capacitance of said semiconductor region may be set equally, respectively.

  In the one aspect described above, the floating diffusion portion may be formed of two semiconductor regions each having a contact portion.

The solid-state imaging device according to another aspect includes a first pixel and a second pixel that are arranged adjacent to each other in the first direction . First and second pixels includes a photoelectric conversion unit for generating a signal charge in accordance with the amount of incident light, a plurality of floating diffusion regions, and a plurality of transfer transistors, respectively. A plurality of floating diffusion regions, as well as storing each generated signal charges by photoelectric conversion unit, are electrically connected with each pixel, it is spaced in a second direction perpendicular to the first direction at each pixel The The plurality of transfer transistors form a pair with each floating diffusion region, and transfer the signal charges from the photoelectric conversion unit to the floating diffusion region in contact therewith. The plurality of transfer transistors of the first pixel are formed on only one side extending in the second direction among the sides of the photoelectric conversion unit of the first pixel. The plurality of transfer transistors of the first pixel and the plurality of floating diffusion regions of the first pixel are disposed between the photoelectric conversion unit of the first pixel and the photoelectric conversion unit of the second pixel. In each pixel, the gates of the plurality of transfer transistors are electrically connected.

The solid-state imaging device according to another aspect includes a first pixel and a second pixel that are arranged adjacent to each other in the first direction. The first pixel and the second pixel include a photoelectric conversion unit that generates a signal charge according to the amount of incident light, a floating diffusion unit that accumulates the signal charge generated by the photoelectric conversion unit, and a floating diffusion unit from the photoelectric conversion unit. One transfer transistor for transferring the signal charge to, a reset transistor for resetting the charge in the floating diffusion portion, an amplification transistor for outputting an electric signal corresponding to the charge in the floating diffusion portion, and selectively passing the electric signal to the signal line A selection transistor to be read. Further, the transfer transistor of the first pixel and the floating diffusion portion of the first pixel are arranged between the photoelectric conversion unit of the first pixel and the photoelectric conversion unit of the second pixel. The transfer transistor of the first pixel is formed along one side extending in the second direction orthogonal to the first direction among the respective sides of the photoelectric conversion unit. The floating diffusion portion of the first pixel has a shape having a plurality of contact portions in contact with the transfer transistor of the first pixel at intervals in the second direction. The reset transistor, the amplification transistor, and the selection transistor of each pixel are arranged in the second direction with respect to the photoelectric conversion unit.
The solid-state imaging device according to another aspect includes a first pixel and a second pixel that are arranged adjacent to each other in the first direction. The first pixel and the second pixel include a photoelectric conversion unit that generates a signal charge according to the amount of incident light, a plurality of floating diffusion regions, a plurality of transfer transistors, and a reset transistor that resets the charges in the floating diffusion region. And an amplifying transistor that outputs an electric signal corresponding to the charge in the floating diffusion region, and a selection transistor that selectively reads out the electric signal to the signal line. The plurality of floating diffusion regions accumulate signal charges generated by the photoelectric conversion units, are electrically connected to each pixel, and are arranged at intervals in a second direction orthogonal to the first direction at each pixel. The The plurality of transfer transistors form a pair with each floating diffusion region, and transfer the signal charges from the photoelectric conversion unit to the floating diffusion region in contact therewith. Further, the plurality of transfer transistors of the first pixel are formed only on one side extending in the second direction among the sides of the photoelectric conversion unit of the first pixel. The plurality of transfer transistors of the first pixel and the plurality of floating diffusion regions of the first pixel are disposed between the photoelectric conversion unit of the first pixel and the photoelectric conversion unit of the second pixel. In each pixel, the gates of the plurality of transfer transistors are electrically connected. The reset transistor, the amplification transistor, and the selection transistor of each pixel are arranged in the second direction with respect to the photoelectric conversion unit.

  According to the present invention, it is possible to provide a solid-state imaging device in which occurrence of crosstalk is further suppressed.

1 is a circuit diagram illustrating a schematic configuration of a solid-state imaging device according to an embodiment. The figure which shows the example of the planar structure of pixel PX in one Embodiment The figure which shows the circuit structural example of the pixel PX in one Embodiment. 1 is a schematic diagram showing a cross section of a solid-state imaging device according to an embodiment. The figure which shows the comparative example of FIG. The figure which shows the example of the planar structure of pixel PX in other embodiment.

<Description of One Embodiment>
FIG. 1 is a diagram illustrating a schematic configuration example of a solid-state imaging device according to an embodiment. The solid-state imaging device of one embodiment is formed as a CMOS type solid-state imaging device on a silicon substrate using a CMOS process, and is mounted on, for example, a digital still camera or a video camera.

  The solid-state imaging device includes a plurality of pixels PX arranged in a matrix, a vertical scanning unit 11, a signal storage unit 12, a horizontal scanning unit 13, and a vertical output line 14 provided for each column of pixels PX. The constant current source 15 is connected to each vertical output line 14, and a pair of transfer gates 16 a and 16 b for connecting each vertical output line 14 to the signal storage unit 12. Here, in FIG. 1, only 3 × 2 pixels PX are shown for simplicity, but it goes without saying that a larger number of pixels are arranged on the light receiving surface of an actual solid-state imaging device.

  The vertical scanning unit 11 outputs a selection pulse φSEL, a reset pulse φRES, and a transfer pulse φTX to the pixel groups arranged in the horizontal direction in FIG. The pulses φSEL, φRES, and φTX have a high logic level of the power supply voltage VDD and a low logic level of the ground voltage VSS. The signal accumulation unit 12 sequentially accumulates a noise signal output from each pixel PX of the pixel group arranged in the horizontal direction in FIG. 1 and a pixel signal on which the noise signal is superimposed. The horizontal scanning unit 13 controls the operation of the signal storage unit 12 by the control pulse φH, and sequentially outputs the signals stored in the signal storage unit 12 to a not-shown correlated double sampling circuit (CDS circuit) or the like.

  The constant current source 15 supplies a current to the vertical output line 14 in order to read out the image signal. The transfer gates 16a and 16b are formed by nMOS transistors. The transfer gate 16a is turned on in synchronization with the signal transfer pulse φTS in order to transfer the pixel signal on which the noise signal is superimposed to the signal storage unit 12. The transfer gate 16b is turned on in synchronization with the noise transfer pulse φTN in order to transfer the noise signal to the signal storage unit 12. Signal transfer pulse φTS and noise transfer pulse φTN are control signals for operating the correlated double sampling circuit.

  FIG. 2 is a diagram illustrating an example of a planar structure of the pixel PX. FIG. 3 is a diagram illustrating a circuit configuration example of the pixel PX. Here, the shaded area in FIG. 2 indicates the gate of the transistor. A chain line frame in FIG. 2 indicates a layout area of the pixel PX. In FIG. 2, illustration of the control wiring for supplying the pulses φSEL, φRES, and φTX and the wiring for the power supply VDD are omitted.

  The pixel PX includes a photodiode PD, a transfer transistor TX, a reset transistor RES, an amplification transistor AMP, a selection transistor SEL, and two floating diffusion regions FD1 and FD2. Note that all the transistors formed in the pixel PX are nMOS transistors.

  In FIG. 2, one transfer transistor TX is disposed on one side of a rectangular photodiode PD. Further, one end (contact portion) of floating diffusion regions FD1 and FD2 arranged in parallel in the vertical direction is connected to the transfer transistor TX. The floating diffusion regions FD1 and FD2 are arranged so as to be symmetrical with respect to the center in the vertical direction of the photodiode PD. Note that the photodiode PD, the transfer transistor TX, and the floating diffusion regions FD1 and FD2 arranged in parallel are arranged in a line in the horizontal direction of FIG.

  Said photodiode PD produces | generates a signal charge according to the light quantity of incident light. The transfer transistor TX is turned on during the high level period of the transfer pulse φTX, and transfers the signal charge accumulated in the photodiode PD to the floating diffusion regions FD1 and FD2. In FIG. 3, one transfer transistor TX is apparently represented as two transistors that are driven synchronously.

  The source of the transfer transistor TX is also a photodiode PD, and the drain of the transfer transistor TX is the floating diffusion regions FD1 and FD2. These floating diffusion regions FD1 and FD2 are N diffusion regions formed by introducing impurities into the semiconductor substrate. The capacities of the two floating diffusion regions FD1 and FD2 are set to be equal to each other.

  The floating diffusion regions FD1 and FD2 are connected to the gate of the amplification transistor AMP and the source of the reset transistor RES, respectively, by connection wiring (copper wiring or aluminum wiring).

  In FIG. 2, the selection transistor SEL, the amplification transistor AMP, and the reset transistor RES are arranged in a line along the line in which the photodiode PD, the transfer transistor TX, and the floating diffusion regions FD1 and FD2 are arranged. The selection transistor SEL, the amplification transistor AMP, and the reset transistor RES are formed by disposing gates at predetermined intervals on one active region extending in the horizontal direction in FIG. The amplification transistor AMP and the reset transistor RES have a common drain connected to the power supply line VDD. With this arrangement, in one embodiment, the source / drain of the selection transistor SEL, the amplification transistor AMP, and the reset transistor RES can be made common, and the layout size of each pixel can be minimized.

  The reset transistor RES is turned on during the high level period of the reset pulse φRES, and resets the floating diffusion regions FD1 and FD2 to the power supply voltage VDD. The amplification transistor AMP has a drain connected to the power supply voltage VDD, a gate connected to the floating diffusion regions FD1 and FD2, a source connected to the drain of the selection transistor SEL, and a force follower having the constant current source 15 as a load. The circuit is configured. The amplification transistor AMP outputs a read current to the output terminal OUT via the selection transistor SEL according to the voltage value of the floating diffusion regions FD1 and FD2. The selection transistor SEL is turned on during the high level period of the selection pulse φSEL, and connects the source of the amplification transistor AMP to the output terminal OUT.

  FIG. 4 is a schematic diagram showing a cross section of the solid-state imaging device in one embodiment. In the solid-state imaging device according to one embodiment, a P-type well 22 is provided on an N-type silicon substrate 21, and a photodiode PD, a transfer transistor TX, a floating diffusion region (FD1, FD2), and the like are provided on the P-type well 22. An element is formed. A silicon oxide film 23 is formed on the upper surface side of the P-type well 22. The photodiode PD shown in FIG. 4 is an embedded type photodiode composed of an N-type charge storage layer provided in the P-type well 22 and a P-type depletion prevention layer disposed on the surface side thereof. is there.

  Each pixel PX is provided with a microlens 24 and a color filter 25 in order from the top. The color filter 25 may be configured by arranging, for example, R, G, and B color filters in a Bayer array or a stripe array, or a complementary color system (for example, magenta, green, cyan, and yellow) is used. System) color filter array may be used. In the wiring portion of the pixel PX, incident light is shielded by the light shielding aluminum film 26 disposed on the upper surface.

  Hereinafter, the operation of the solid-state imaging device in one embodiment will be described. The light incident on the light receiving surface of the solid-state imaging device passes through the microlens and the color filter and reaches the photodiode PD of each pixel. At this time, photoelectric conversion is slightly performed even at a position deep from the surface of the semiconductor (a peripheral portion of the photodiode PD) by light obliquely incident on the light receiving surface. Since electrons move outside the depletion layer by diffusion, the direction of electron movement is uncertain if the impurity concentration of the P-type well 22 is uniform. Therefore, electrons photoelectrically converted at a deep position of the photodiode PD are absorbed even in a diffusion region having a higher potential such as a floating diffusion region, but are mixed into adjacent pixels with a certain probability to cause crosstalk (see FIG. 4).

  FIG. 5 is a schematic diagram showing a comparative example of FIG. Since the comparative example of FIG. 5 has the same configuration as that of FIG. 2 except that there is one floating diffusion region connected to the transfer transistor TX, the duplicate description is omitted. In the case of the comparative example shown in FIG. 5, P diffusion regions (regions surrounded by broken lines in FIG. 5) are formed on both sides of the floating diffusion region (FD). The Therefore, electrons generated in the vicinity of the P diffusion region indicated by the broken line in FIG. 5 easily pass through the side of the floating diffusion region and easily reach adjacent pixels.

  On the other hand, in the case of one embodiment, the floating diffusion region having a contact portion with the transfer transistor TX is divided into two and arranged in parallel (see FIG. 2). In the case of one embodiment, the space of the P diffusion region indicated by a broken line is smaller than that in the comparative example in FIG.

  Therefore, in the configuration of the embodiment, even when the total capacity of the floating diffusion region is the same as that of the comparative example, electrons generated in the peripheral portion of the photodiode PD are more easily absorbed by the floating diffusion region. Therefore, fewer electrons pass through the side of the floating diffusion region and reach the adjacent pixels. Therefore, according to one embodiment, the occurrence of crosstalk can be effectively suppressed without increasing the capacity of the floating diffusion region.

<Description of other embodiments>
FIG. 6 is a diagram illustrating an example of a planar structure of the pixel PX in another embodiment. Since the other embodiment is a modification of the above-described one embodiment, only the differences from the above-described one embodiment will be described for the configuration in FIG.

  In the pixel PX of another embodiment, two transfer transistors TX and floating diffusion regions FD1 and FD2 are arranged on one side of the rectangular photodiode PD. The two transfer transistors TX and the floating diffusion regions FD1 and FD2 are arranged in parallel vertically. Each transfer transistor is connected to one end of the floating diffusion region FD1 or FD2, and transfers the signal charge from the photodiode PD to the corresponding floating diffusion region FD1, FD2. The gates of the two transfer transistors TX are electrically connected by wiring and are driven in synchronization.

  The floating diffusion regions FD1 and FD2 are connected to the gate of the amplification transistor AMP and the source of the reset transistor RES, respectively, by connection wiring. The circuit configuration of the other embodiments is the same as the example of FIG. Even in the configuration of the other embodiment, substantially the same effect as that of the first embodiment can be obtained.

<Supplementary items of the embodiment>
(1) In the above embodiment, the example in which the floating diffusion region is divided into two and arranged in parallel has been described. However, the present invention is not limited to the configuration of the above embodiment. For example, the floating diffusion region may be divided into three or more and arranged in parallel. Further, both ends of one floating diffusion region formed in a C shape may be connected to one transfer transistor TX, and the floating diffusion region and the transfer transistor TX may be arranged in a ring shape (in either case) Is also omitted).

  (2) In the above embodiment, the floating diffusion regions may be arranged in parallel so as to be asymmetric with respect to the center of the photodiode PD.

  From the above detailed description, features and advantages of the embodiments will become apparent. It is intended that the scope of the claims extend to the features and advantages of the embodiments as described above without departing from the spirit and scope of the right. Further, any person having ordinary knowledge in the technical field should be able to easily come up with any improvements and modifications, and there is no intention to limit the scope of the embodiments having the invention to those described above. It is also possible to use appropriate improvements and equivalents within the scope disclosed in.

DESCRIPTION OF SYMBOLS 11 ... Vertical scanning part, 12 ... Signal storage part, 13 ... Horizontal scanning part, 14 ... Vertical output line, 15 ... Constant current source, 16a, 16b ... Transfer gate, 21 ... N type silicon substrate, 22 ... P type well, 23 ... Silicon oxide film, 24 ... Micro lens, 25 ... Color filter, 26 ... Light shielding aluminum film, PX ... Pixel, PD ... Photodiode, TX ... Transfer transistor, RES ... Reset transistor, AMP ... Amplification transistor, SEL ... Selection transistor , FD, FD1, FD2 ... floating diffusion region

Claims (7)

A first pixel and a second pixel arranged adjacent to each other in the first direction ;
The first pixel and the second pixel are:
A photoelectric conversion unit that generates a signal charge according to the amount of incident light; and
A floating diffusion unit for accumulating the signal charges generated by the photoelectric conversion unit;
Wherein one of the transfer transistors for transferring the signal charges to the floating diffusion portion from the photoelectric conversion unit, respectively,
The transfer transistor of the first pixel and the floating diffusion part of the first pixel are disposed between the photoelectric conversion part of the first pixel and the photoelectric conversion part of the second pixel,
The transfer transistor of the first pixel is formed along one side extending in a second direction orthogonal to the first direction among the sides of the photoelectric conversion unit,
The solid-state imaging device , wherein the floating diffusion portion of the first pixel has a shape having a plurality of contact portions in contact with the transfer transistor of the first pixel at intervals in the second direction . The solid-state imaging device according to claim 1,
The solid-state imaging device, wherein the contact portions of the floating diffusion portion are arranged so as to be symmetrical with respect to a center of a side extending in the second direction of the photoelectric conversion portion. The solid-state imaging device according to claim 1 or 2,
The floating diffusion portion is composed of a plurality of semiconductor regions each having the contact portion,
A solid-state imaging device, wherein the semiconductor regions have equal capacitances. In the solid-state image sensor according to any one of claims 1 to 3,
The solid state imaging device, wherein the floating diffusion portion is composed of two semiconductor regions each having the contact portion. A first pixel and a second pixel arranged adjacent to each other in the first direction ;
The first pixel and the second pixel are:
A photoelectric conversion unit that generates a signal charge according to the amount of incident light; and
Each of the signal charges generated by the photoelectric conversion unit is stored , and is electrically connected to each pixel, and a plurality of floating elements are arranged at intervals in a second direction orthogonal to the first direction in each pixel. Diffusion area,
A plurality of transfer transistors that form pairs with each of the floating diffusion regions and respectively transfer the signal charges from the photoelectric conversion unit to the floating diffusion regions that are in contact with each other ,
The plurality of transfer transistors of the first pixel are formed only on one side extending in the second direction among the sides of the photoelectric conversion unit of the first pixel,
The plurality of transfer transistors of the first pixel and the plurality of floating diffusion regions of the first pixel are disposed between the photoelectric conversion unit of the first pixel and the photoelectric conversion unit of the second pixel,
In each pixel, the gates of the plurality of transfer transistors are electrically connected, respectively . A first pixel and a second pixel arranged adjacent to each other in the first direction ;
The first pixel and the second pixel are:
A photoelectric conversion unit that generates a signal charge according to the amount of incident light; and
A floating diffusion unit for accumulating the signal charges generated by the photoelectric conversion unit;
One transfer transistor for transferring the signal charge from the photoelectric conversion unit to the floating diffusion unit;
A reset transistor for resetting the charge of the floating diffusion portion;
An amplification transistor that outputs an electrical signal corresponding to the charge of the floating diffusion portion;
Includes a selection transistor for reading selectively the signal lines the electrical signal, respectively,
The transfer transistor of the first pixel and the floating diffusion part of the first pixel are disposed between the photoelectric conversion part of the first pixel and the photoelectric conversion part of the second pixel,
The transfer transistor of the first pixel is formed along one side extending in a second direction orthogonal to the first direction among the sides of the photoelectric conversion unit,
The floating diffusion portion of the first pixel has a shape having a plurality of contact portions in contact with the transfer transistor of the first pixel at intervals in the second direction ,
The solid-state imaging device , wherein the reset transistor, the amplification transistor, and the selection transistor of each pixel are arranged in the second direction with respect to the photoelectric conversion unit . A first pixel and a second pixel arranged adjacent to each other in the first direction ;
The first pixel and the second pixel are:
A photoelectric conversion unit that generates a signal charge according to the amount of incident light; and
Each of the signal charges generated by the photoelectric conversion unit is stored, and is electrically connected to each pixel, and a plurality of floating elements are arranged at intervals in a second direction orthogonal to the first direction in each pixel. Diffusion area,
A plurality of transfer transistors that pair with each of the floating diffusion regions and transfer the signal charges from the photoelectric conversion unit to the floating diffusion regions that are in contact with each other;
A reset transistor for resetting the charge in the floating diffusion region;
An amplification transistor that outputs an electrical signal corresponding to the charge of the floating diffusion region;
Includes a selection transistor for reading selectively the signal lines the electrical signal, respectively,
The plurality of transfer transistors of the first pixel are formed only on one side extending in the second direction among the sides of the photoelectric conversion unit of the first pixel,
The plurality of transfer transistors of the first pixel and the plurality of floating diffusion regions of the first pixel are disposed between the photoelectric conversion unit of the first pixel and the photoelectric conversion unit of the second pixel,
In each pixel, the gates of the plurality of transfer transistors are electrically connected to each other ,
The solid-state imaging device , wherein the reset transistor, the amplification transistor, and the selection transistor of each pixel are arranged in the second direction with respect to the photoelectric conversion unit .

Images